1. Field of the Invention
The present invention relates to a high vacuum valve for opening/closing a transport passage and a discharge passage for the vacuum (negative pressure). In particular, the present invention relates to a high vacuum valve which is arranged, for example, for a transport passage when a workpiece such as a wafer, an integrated circuit (IC), or a part thereof is transported from one vacuum processing chamber to another vacuum processing chamber, and/or which is arranged, for example, for a discharge passage for connecting a high vacuum processing chamber and a vacuum pump.
2. Description of the Related Art
A high vacuum valve for a transport passages is known (see, for example, Japanese Laid-Open Patent Publication No. 9-303577), in which a first opening and a second opening are formed at a front surface wall and a back surface wall of a main valve body having a valve chamber (chamber) at the inside respectively, a valve seat is formed at an inner portion of the first opening or the second opening, a valve plug (gate, blade) is connected to a proximal end of a valve shaft for performing rectilinear motion, and the valve plug is pressed against the valve seat to close the valve. In the high vacuum valve, the valve shaft is inserted into a central bore of an upper wall of the entire valve in a non-contact state. A side surface portion of the valve shaft disposed outside the valve chamber is covered with a bellows in a non-contact state. An air-tight state is established between the forward end of the bellows and the forward end of the valve shaft, and an air-tight state is established between the proximal end of the bellows and the surroundings of the central bore of the upper wall.
The high vacuum valve (gate valve) for the transport passage as described above is constructed such that the valve plug arrives at the position opposed to the valve seat in accordance with the rectilinear motion of the valve shaft, and then the valve plug is pressed against the valve seat in accordance with the swinging motion of the valve shaft. The following mechanism is used as a mechanism for pressing the valve plug against the valve seat. That is, an engaging section, which has a front surface and a back surface, is formed at the forward end of the valve shaft. The front surface and the back surface of the engaging section are engaged with a first engaging roller and a second engaging roller each of which is rotatably supported by a roller support member. When a support point roller, which is connected to the forward end of the valve shaft, is supported at a proximal end of a support point groove, the roller support member is moved frontwardly to engage the first engaging roller with the front surface engaging section. Accordingly, the valve shaft makes the swinging movement in the direction to press the valve plug against the valve seat.
A high vacuum valve (L-type valve) for a discharge passage involves the following problem. That is, when the temperature is not more than a certain temperature, a reaction product of a reaction gas adheres to the interior of the high vacuum valve, and it becomes difficult to control the high vacuum valve. It is required to realize a uniform temperature, for example, for an upper portion of a valve body, a valve flange of the valve body, a bellows-side flange of the valve body, and the outside portion of the valve.
Conventionally, in order to maintain a predetermined temperature or a higher temperature for the high vacuum valve, an aluminum material having a high coefficient of thermal conductivity is used for the body and the bonnet, a stainless steel material is used for the valve plug and the bellows, and a heater is attached to the outside of the body. In the case of such an arrangement, the body and the bonnet are allowed to make tight contact therebetween, the heat of the body is transferred to the bonnet made of the aluminum material, and the heat is transferred from the bonnet to the bellows and the valve plug.
On the other hand, although the aluminum material has the high coefficient of thermal conductivity, it is poor in strength and corrosion resistance. Therefore, it is demanded that the stainless steel material (SUS), which is excellent in strength and corrosion resistance, is used for the body. Accordingly, a high vacuum valve has been manufactured, which has the same structure and the same size provided that the material for the body is changed from the aluminum material to the SUS material. The temperature distribution of the high vacuum valve, which is obtained when the electricity is applied by a heater, is greatly dispersed concerning temperature depending on the measuring point, because the coefficient of thermal conductivity of the SUS material is about {fraction (1/12)} of that of the aluminum material. In the case of such a high vacuum valve, it is difficult to avoid the deposit (adhesion of the reaction product).
In the case of the high vacuum valve for the discharge passage described above, for example, in order to take out an wafer from the vacuum chamber to the atmospheric air, an inert gas such as nitrogen gas is introduced into the vacuum chamber in the vacuum state to break the vacuum state. During this process, the dust (particle), which adheres to the floor surface and the wall surface in the vacuum chamber and the piping is raised by the injected gas, and it floats over the interior of the chamber and the pipe, resulting in adhesion to the wafer to badly affect the performance of the semiconductor. If the dust continuously stays at the adhered portion, no special trouble occurs. Therefore, in order to avoid the floating of the dust during the breakage of the vacuum, an apparatus for gradually increasing the gas flow rate is used.
The problem of the adhesion of the reaction product (dust) by the reaction gas is not limited to the high vacuum valve for the discharge passage. The problem also arises in the high vacuum valve for the transport passage. In order to avoid the adhesion of the dust, the outer portion of the valve chamber has been hitherto heated with a heater. When the outer portions of the main valve body or the valve body are heated, the valve plug and the shaft of the high vacuum valve (gate valve) for the transport passage and the valve plug and the bellows of the high vacuum valve (L-type valve) for the discharge passage receive the radiant heat from the surroundings.
However, the high vacuum valve has a valve plug-driving section (actuator) in a low temperature state for displacing the valve plug. The heat, which is transferred to the valve plug, escapes through the valve shaft toward the valve plug-driving section at the low temperature. When the heater is arranged at the outside or the inside of the main valve body or the valve body to further heat the valve plug with the heater, a problem arises in an insulating member of a lead wire of the heater due to the high temperature.
An object of the present invention is to provide a high vacuum valve for a transport passage, which makes it possible to avoid the transfer of the heat of a valve plug to a low temperature portion from the valve plug via a valve shaft and which makes it possible to simplify a mechanism for swinging the valve to press the valve plug against a valve seat.
Another object of the present invention is to provide a high vacuum valve which makes it possible to obtain a uniform temperature distribution by broadly dispersing the heat from a heater by using, for a main valve body or a body, a stainless steel material having strength and corrosion resistance.
According to a first aspect of the present invention, there is provided a high vacuum valve comprising a first opening and a second opening formed through a front surface wall and a back surface wall of a main valve body having a valve chamber at the inside respectively; a valve seat formed at an inner portion of the first opening or the second opening; and a valve plug connected to a proximal end of a valve shaft for making rectilinear motion; the valve shaft being inserted in a non-contact state into a central bore of an upper wall of the main valve body; a side surface of the valve shaft at the outside of the valve chamber being covered with a bellows in a non-contact state; an air-tight state being given between a forward end of the bellows and a forward end of the valve shaft; and an air-tight state being given between a proximal end of the bellows and surroundings of the central bore of the upper wall; in which the valve plug arrives at a position opposed to the valve seat in accordance with the rectilinear motion of the valve shaft; and then the valve plug is pressed against the valve seat in accordance with swinging motion of the valve shaft to close a valve; wherein a heater is arranged in a tight contact manner in the valve shaft; and a wiring line for supplying electric power from the outside of the high vacuum valve is connected to the heater.
According to a second aspect of the present invention, there is provided a high vacuum valve comprising a plurality of ports formed to make communication with a valve chamber of a valve body via tubes; a bonnet connected to an upper portion of the valve body; and a valve seat formed at a flow passage for connecting the valve chamber to one of the tubes; the flow passage being closed by allowing a valve plug to make contact with the valve seat; and the flow passage being opened by allowing the valve plug to make separation from the valve seat; in which a valve shaft fixed to the valve plug is inserted through a central bore of the bonnet; wherein a heater is arranged in a tight contact manner in the valve shaft; and a wiring line for supplying electric power from the outside of the high vacuum valve is connected to the heater.
According to a third aspect of the present invention, there is provided a high vacuum valve comprising a first opening and a second opening formed through a front surface wall and a back surface wall of a main valve body having a valve chamber at the inside respectively; a valve seat formed at an inner portion of the first opening or the second opening; and a valve plug connected to a proximal end of a valve shaft for making rectilinear motion; the valve shaft being inserted in a non-contact state into a central bore of an upper wall of the main valve body; a side surface of the valve shaft at the outside of the valve chamber being covered with a bellows in a non-contact state; an air-tight state being given between a forward end of the bellows and a forward end of the valve shaft; and an air-tight state being given between a proximal end of the bellows and surroundings of the central bore of the upper wall; in which the valve plug arrives at a position opposed to the valve seat in accordance with the rectilinear motion of the valve shaft; and then the valve plug is pressed against the valve seat in accordance with swinging motion of the valve shaft to close a valve; wherein a cap member is connected to an upper portion of the valve shaft; support point rollers connected to lower portions of the cap member are engaged with support point grooves; guide rollers connected to upper portions of the cap member are engaged with cam grooves of a transmission member; the transmission member is movable downwardly to move the guide rollers along the cam grooves when the support point rollers are located at proximal ends of the support point grooves; and thus the valve shaft makes swinging movement in a direction to press the valve plug against the valve seat.
According to a fourth aspect of the present invention, there is provided the high vacuum valve as defined in the first aspect; wherein a cap member is connected to an upper portion of the valve shaft; support point rollers connected to lower portions of the cap member are engaged with support point grooves; guide rollers connected to upper portions of the cap member are engaged with cam grooves of a transmission member; the transmission member is movable downwardly to move the guide rollers along the cam grooves when the support point rollers are located at proximal ends of the support point grooves; and thus the valve shaft makes swinging movement in a direction to press the valve plug against the valve seat.
According to a fifth aspect of the present invention, there is provided the high vacuum valve as defined in the third or fourth aspect; wherein the transmission member is connected to output shafts of actuators; the transmission member and the cap member are connected to one another by the aid of guide rods so that they are not separated from each other by a space therebetween of not less than a preset distance; a spring is installed between the transmission member and the cap member; and the transmission member and the cap member are urged in directions to make separation from each other.
According to a sixth aspect of the present invention, there is provided the high vacuum valve as defined in the first or fifth aspect; wherein the main valve body or the valve body is arranged with a single heater or a plurality of heaters.
According to a seventh aspect of the present invention, there is provided a high vacuum valve comprising a heating unit including a body made of stainless steel arranged with a single heater or a plurality of heaters; a single sheet or a plurality of sheets of heat conduction plates made of metal having a high coefficient of thermal conductivity arranged in a tight contact manner on a surface of the body; and the heater arranged on a surface of each of the heat conduction plates; wherein an entire surface of the heat conduction plate and a surface of the body are covered with a cover made of a heat-insulating material while being separated therefrom by a predetermined spacing distance; heat from the heater having a small heating area is transferred over a wide range of the body via the heat conduction plate; a natural convection is generated in a closed space between the cover and the body; and the heat is transferred over the wide range of the body in accordance with natural convection heat transfer. The predetermined spacing distance referred to above is a spacing distance which is suitable to generate the natural convection.
According to an eighth aspect of the present invention, there is provided the high vacuum valve as defined in the seventh aspect; wherein the heater to be used is a thermistor, and the heat conduction plate to be used is made of copper or aluminum.